The present invention relates to a method for piloting electromagnetic actuators for the control of the valves of an engine.
As is known, internal combustion engines are currently at the experimental stage, in which the intake and discharge valves are moved by electromagnetic actuators (of the type described in European patent application EP1087110). These electromagnetic actuators have undoubted advantages, since they make it possible to control each valve according to an optimized law for any operative condition of the engine, whereas the conventional mechanical actuators (typically cam shafts) require definition of a raising profile of the valves which represents an acceptable compromise for all the possible operating conditions of the engine.
An electromagnetic actuator for a valve of an internal combustion engine of the above-described type normally comprises an actuator body, which is connected to the stem of the valve and in conditions of rest is maintained by at least one spring in an intermediate position between two de-excited electromagnets; in use, the electromagnets are controlled such as to exert alternately a force of attraction of magnetic origin on the actuator body in order to displace the actuator body itself between the two end stop positions, which correspond to a position of maximum opening and of closure of the respective valve.
The electromagnets of the electromagnetic actuators are piloted by a common piloting device, which is supplied by the electrical generation system of the vehicle, which normally consists of an electrolytic battery and a direct current generator which is connected mechanically to the drive shaft. In particular, each electromagnet is piloted by the common piloting device by means of the supply of an electric current wave which has two, initial and end control portions in which the intensity of the electric current varies rapidly and an intermediate maintenance portion in which the intensity of the electric current remains substantially constant and equal to a maintenance value; the control portions of an electric current wave are disposed at the start of the wave, when the electric current passes from the zero value to the maintenance value by means of a pulse which has a higher peak than the maintenance value, and at the end of the wave, when the electric current passes from the maintenance value to the zero value.
At each control portion, there is a pulse variation of the quantity of electric charge distributed overall by the piloting device which involves substantially identical pulse variation of the quantity of electric charge supplied to the piloting device by the electrical generation system of the vehicle; it has been observed that the generator cannot cope with this pulse variation of electric charge owing to the speed of this variation, which must be absorbed entirely by the battery.
However, it has been observed experimentally that a battery which is subjected continually to the above-described pulse variations of electric charge distributed deteriorates very quickly, and in practice has a service life which is no greater than 5-6 months, compared with a normal service life of at least 3-4 years.
In order to try to eliminate the above-described disadvantage, it has been proposed to place in parallel with the piloting device a capacitor bank, which can absorb the pulse variations of electric charge in place of the battery. However, in order to be efficient this solution requires the installation of very high overall capacities (indicatively between 3 and 8 mF), which require use of electrolytic capacitors which are costly, cumbersome, and relatively unreliable in a hostile environment such as the engine compartment.
The object of the present invention is to provide a method for piloting electromagnetic actuators for control of the valves of an engine, which is free from the above-described disadvantages and, in particular, is easy and economical to implement.
According to the present invention, a method for piloting electromagnetic actuators for control of the valves of an engine is provided; each electromagnetic actuator comprising at least one respective electromagnet, which is piloted by a common piloting device by means of supply of an electric current wave which has at least one control portion in which the intensity of the electric current varies rapidly and a maintenance portion in which the intensity of the electric current remains substantially constant; the method consisting of supplying respective electric current waves cyclically to the electromagnets in order to control the valves according to the drive point; the method being characterized in that at the control portion of each electric current wave there is variation of the value of the intensity of the electric current supplied during the portions of maintenance of the other electric current waves in order to limit the variation of the quantity of electric charge distributed overall by the piloting device.